With spring only two days away, a stink bug crawls on newly- blossomed bright yellow crocuses Thursday, March 18, 2010, in Newtown, Pa.

The creature with no known natural predators in this country that has invaded homes in about two dozen states since 1998 is being stalked by a new predator.

A tiny parasitic wasp — a creature smaller than a gnat and smaller even than a fruit fly — is showing promise at a laboratory here as a possible biological control.

The wasp, in the genus Trissolcus, may be able to nip the stink bug explosion in the bud by preying on stink bug eggs. These wasps are a non-stinging species.

Brown marmorated stink bugs lay especially beautiful egg clusters — sea green with exactly 27 to 28 eggs in each mass. The assemblage of eggs looks a little like a one-dimensional view of a stack of cannon balls.

In Japan, Korea and China, where the brown marmorated stink bug is a native, these Trissolcus wasps track down the eggs, lay a single egg of their own in each of the stink bug eggs and then move on in search of more.

As the days pass, a larval wasp — wormlike and tiny — develops and grows, eating away at the developing stink bug. Then, one day, it breaks through the top of the egg as a full-grown wasp.

Like in the movie "Alien," "it consumes the host from the inside," said Kim Hoelmer, a research entomologist at the U.S. Department of Agriculture's Beneficial Insects Introduction Research Unit here.

It is here that Hoelmer and his research assistant, Kathy Tatman, work to keep a collection of the wasps and the stink bugs alive so they can test the potential for a predator-prey control.

The stink bugs, first identified in Allentown, Pa., are mainly a nuisance, seeking shelter in homes once the weather turns cooler each fall.

Concern is growing, however, that the brown marmorated stink bug could become an agricultural pest.

In the Newark, Del., lab, Tatman feeds the caged bugs string beans, carrots, grapes, squash and apples. She has both holly and Paulownia tree seedlings in the cages. In Asia, the insects are a pest for soybean pods and in fruit orchards.

Scientists suspect the insects first arrived in the United States — possibly as early as 1996 — in packing materials used for shipping.

Once the stink bugs arrived, they began to move, sometimes transported by vehicle as people went from place to place. Stink bugs also can fly, Hoelmer said.

As the insects moved and the population expanded, researchers like Hoelmer and Tatman have tried to answer that question.

They took dozens of stink bug egg cases out into the field to see if the eggs would be targeted by any native parasitic insects, Hoelmer said.

It turns out there are a few native predators that could find and target the brown marmorated stink bug egg cases. But only about 2% to 5% of the native parasites find the stink bugs, Hoelmer said.

"That's not enough to keep the brown marmorated stink bugs under control," he said.

The next step was to see what insect predators target the brown marmorated stink bugs in Asia, he said. There, where both the brown marmorated stink bug and the Trissolcus wasps are natives, the wasps help keep the stink bug population in check.

It isn't just a matter of importing a bunch of fly-speck-sized wasps to solve the invasion of the stink bug, however.

There are good stink bugs, native varieties that prey on harmful insects. So Hoelmer said scientists don't want to introduce a new, non-native insect that could kill off the good ones.

Tatman is conducting trials on four species of Trissolcus wasps to see how well they target the brown marmorated stink bug egg masses in a quarantined, lab setting. If all goes well, federal officials could one day approve the tiny wasps as a natural control for brown marmorated stink bugs.

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How to kill stink bugs

You may be tempted to crush them, but you'll be rewarded with an odor you won't like. Instead:

- Vacuum them. This also will help kill stink bug eggs. But dispose of the vacuum bag, maybe dousing it with some insecticide as you set it in the trash can.

- Attract them. Use a wide-mouth can. Fill with an inch of water, sweet-scented dish soap, and a little cooking oil on top. Make sure that pets cannot lick this trap. The sweet smell lures the bugs; the oil smothers their discharge; the soapy water smothers them as they sink.

- Exterminate them with commercially available insecticides. But apply the chemicals outside. If you do so when they are in your walls, you could attract carpet beetles that feed on their carcasses and potentially your woolens.

- Repel them. They don't like the smell of garlic — if you can handle it.

- Block them. Caulk small openings and cracks in your house or elsewhere to keep them out of structures. Repair damaged screens.

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